C4.2 Transfers of energy and matter

What is an ecosystem?

An ecosystem is composed of all the organisms in an area together with their abiotic environment.

What are the two main types of systems?

Open systems and closed systems.

What is an open system?

A system where resources, including chemical substances and energy, can enter or exit.

What is a closed system?

A system where energy can enter or exit, but chemical resources cannot be removed or replaced.

What is the initial source of energy for most ecosystems?

Sunlight.

What organisms carry out photosynthesis?

Cyanobacteria, plants, and eukaryotic algae.

What are producers?

Organisms that fix energy from sunlight into carbon compounds.

Why does the Sahara Desert have little energy harvested despite high sunlight intensity?

Because there are few producers.

Why is more energy available in redwood forests despite lower sunlight intensity?

Because producers are abundant and photosynthesis rates are high.

Why does light penetration decrease in marine and freshwater ecosystems?

Due to the presence of living organisms and non-living matter.

How deep does light penetrate in open oceans?

Little or no light at depths greater than 200 m.

What reduces light penetration in coastal waters?

Suspended clay, silt, and dense populations of phytoplankton.

What provides energy to ecosystems in the darkness of caves?

Dead organic matter carried by streams or chemosynthetic archaebacteria.

Where is Movile Cave located?

Near the Black Sea coast in Romania.

What is chemosynthesis?

The synthesis of carbon compounds using energy from chemical reactions.

What organisms in Movile Cave carry out chemosynthesis?

Archaebacteria.

What is a food chain?

A sequence of organisms, each of which feeds on the previous one.

What are primary consumers?

Organisms that feed on producers.

What are secondary consumers?

Organisms that feed on primary consumers.

What are tertiary consumers?

Organisms that feed on secondary consumers.

What do the arrows in a food chain indicate?

The direction of energy flow.

What is a food web?

A model summarizing all the possible food chains in a community.

What is an apex predator?

A predator that has no natural predators in its ecosystem.

What is an example of an apex predator in the Monte Desert?

The puma (Puma concolor).

Why are food webs more complex than food chains?

Because many consumers feed on more than one species.

What happens to dead organisms in an ecosystem?

They become a source of energy for other organisms.

What are saprotrophs?

Organisms that secrete digestive enzymes into dead organic matter and digest it externally.

What is another name for saprotrophs?

Decomposers.

What are the two main groups of decomposers?

Bacteria and fungi.

What happens to a tree trunk on the forest floor due to decomposers?

It gradually softens and crumbles away.

Why are decomposers important?

They recycle chemical elements by breaking down dead organic matter.

What are autotrophs?

Organisms that make their own carbon compounds from simple inorganic substances.

What are the two types of autotrophs?

Photoautotrophs and chemoautotrophs.

What do photoautotrophs use as an energy source?

Light.

What do chemoautotrophs use as an energy source?

Exothermic inorganic chemical reactions.

What are cyanobacteria?

A type of photoautotrophic bacteria.

What is the primary energy source for most ecosystems?

Sunlight.

What is the Calvin cycle?

A process used by autotrophs to fix carbon dioxide into carbon compounds.

What are iron-oxidizing bacteria?

Chemoautotrophs that obtain energy from oxidizing iron.

What is an example of an iron-oxidizing bacterium?

Acidithiobacillus ferrooxidans.

What do heterotrophs do?

Obtain carbon compounds from other organisms.

What is assimilation?

The process of absorbing carbon compounds and making them part of the body.

How do guanacos obtain amino acids?

By digesting proteins from the leaves of tara bushes.

What are the two types of digestion in heterotrophs?

Internal and external digestion.

What are saprotrophs?

Organisms that digest food externally.

What are consumers?

Organisms that ingest their food.

What is the main function of ATP?

To provide energy for vital cellular activities.

What are three uses of ATP in cells?

Synthesizing molecules, active transport, and movement.

What is cell respiration?

The process of oxidizing carbon compounds to produce ATP.

What are trophic levels?

Groups of organisms classified by how they obtain energy.

What do primary consumers eat?

Producers.

What do secondary consumers eat?

Primary consumers.

Why do higher trophic levels have less energy available?

Due to energy losses between trophic levels.

What are three main forms of energy loss in trophic levels?

Incomplete consumption, incomplete digestion, and cell respiration.

What is incomplete consumption?

When organisms do not consume entire organisms.

What is an example of incomplete consumption?

Predators not eating bones or hair.

What is incomplete digestion?

When not all ingested food is digested and absorbed.

What happens to indigestible material?

It is egested as feces.

What is the primary waste product of cell respiration?

Carbon dioxide and water.

Why do higher trophic levels have smaller biomass?

Due to energy losses at each level.

What percentage of energy is typically lost between trophic levels?

About 90%.

What is the second law of thermodynamics?

Energy transformations are never 100% efficient.

What is the final form of all energy in an ecosystem?

Heat.

What is the main source of heat in living organisms?

Cell respiration.

How do birds and mammals generate heat?

By increasing their rate of heat generation.

How does muscle activity generate heat?

Through ATP usage during contraction.

What happens to heat generated by organisms?

It is lost to the abiotic environment.

What is chemiosmosis?

The process of ATP production using a proton gradient.

What is a major substrate used by chemoautotrophs?

Hydrogen sulfide.

What organisms oxidize sulfur compounds for energy?

Sulfur-oxidizing bacteria.

What is the energy transformation process in ecosystems?

Sunlight → Chemical energy → Heat.

Why do ecosystems rely on continuous energy input?

Because energy is eventually lost as heat.

What is an example of an exothermic inorganic chemical reaction?

Oxidation of iron.

What organisms occupy multiple trophic levels?

Omnivores.

How do saprotrophs obtain nutrients?

By digesting organic matter externally.

What is a major consequence of energy loss in ecosystems?

Fewer organisms at higher trophic levels.

What are detritus feeders?

Organisms that feed on dead organic material.

How do decomposers aid in nutrient cycling?

By breaking down organic matter into inorganic nutrients.

What is primary productivity?

The rate at which producers create biomass.

Why are decomposers crucial for ecosystems?

They recycle nutrients.

What are detritivores?

Organisms that ingest dead organic matter.

What is biomass?

The total mass of organisms in a given area.

What is trophic efficiency?

The percentage of energy transferred from one trophic level to the next.

What happens to excess nutrients in an ecosystem?

They are recycled by decomposers.

What is the main abiotic factor affecting ecosystems?

Availability of sunlight.

Why can't energy be recycled in an ecosystem?

Energy flows through ecosystems and is lost as heat, which eventually radiates into space.

Why do food chains have a limited number of trophic levels?

Energy loss at each trophic level limits the amount of energy available to higher levels.

What is a two-stage food chain example from East Africa?

Elephants eat the tree Senegalia mellifera and are not eaten by predators.

What type of predator is an orca?

An apex predator.

Why don’t food chains continue indefinitely?

There isn’t enough energy left at higher trophic levels to support more consumers.

How do higher trophic level animals compensate for energy loss?

Their prey contains high energy per unit mass, but there is less prey available.

Why do peregrine falcons need large territories?

They require large hunting areas (~100 km²) to find enough food.

What is primary production?

The accumulation of carbon compounds in biomass by autotrophs.

What is gross primary production (GPP)?

The total biomass of carbon compounds produced in plants via photosynthesis.

What is net primary production (NPP)?

GPP minus the biomass lost due to plant respiration.

How is primary production measured?

In grams of carbon per square meter per year (gCm⁻² yr⁻¹).

What is secondary production?

The accumulation of carbon compounds in biomass by heterotrophs.

Why is secondary production lower than primary production?

Energy is lost through respiration at each trophic level.

Why do plant-based diets support more people than meat-based diets?

Crop production yields more energy per hectare than meat production.

What are “pools” in the carbon cycle?

Reservoirs where carbon is stored (e.g., atmosphere, biomass).